According to Piaget's Cognitive-Developmental Theory, Why Should Students Wait Until

According to Piaget's cognitive-developmental theory, why should students wait until high school before studying geometry?

A) Children in earlier grades cannot handle the concrete nature of the problems.
B) Geometry requires abstract thinking which may be difficult for younger children.
C) Geometry requires conservation of mass, which is a difficult concept for younger children.
D) Geometry requires the concept of the imaginary audience, which is NOT achieved until adolescence.